Short-term effect of ascorbate on bacterial content, plasminogen activator inhibitor-1, and myeloperoxidase in septic mice.

BACKGROUND: Sepsis, a potential risk associated with surgery, leads to a systemic inflammatory response including the plugging of capillary beds. This plugging may precipitate organ failure and subsequent death. We have shown that capillary plugging can be reversed rapidly within 1 h by intravenous injection of ascorbate in mouse skeletal muscle. It is unknown whether, in parallel with this effect, ascorbate negatively affects the protective responses to sepsis involving the fibrinolytic and immune systems. We hypothesized that treatment with ascorbate for 1 h does not alter bacterial content, plasminogen activator inhibitor 1 (PAI-1), and neutrophil infiltration in lung, kidney, spleen, and liver (organs with high immune response) of septic mice. MATERIALS AND METHODS: Sepsis was induced by feces injection into the peritoneum. Mice were injected intravenously with ascorbate at 6 h (10 mg/kg), and samples of peritoneal fluid, arterial blood, and organs collected at 7 h were subjected to analyses of bacterial content, PAI-1 messenger RNA and enzymatic activity, and myeloperoxidase (MPO) (a measure of neutrophil infiltration). RESULTS: Sepsis increased bacterial content in all fluids and organs and increased PAI-1 messenger RNA and enzymatic activity in the lung and liver. Sepsis increased the myeloperoxidase level in the lung and liver, and lowered it in the spleen. Except for decreasing the bacterial content in blood, these responses to sepsis were not altered by ascorbate. CONCLUSIONS: The rapid effect of ascorbate against capillary plugging in the septic mouse skeletal muscle is not accompanied by alterations in PAI-1 or myeloperoxidase responses in the organs with high immune response.

Effect of ascorbate on plasminogen activator inhibitor-1 expression and release from platelets and endothelial cells in an in-vitro model of sepsis.

The microcirculation during sepsis fails due to capillary plugging involving microthrombosis. We demonstrated that intravenous injection of ascorbate reduces this plugging, but the mechanism of this beneficial effect remains unclear. We hypothesize that ascorbate inhibits the release of the antifibrinolytic plasminogen activator inhibitor-1 (PAI-1) from endothelial cells and platelets during sepsis. Microvascular endothelial cells and platelets were isolated from mice. Cells were cultured and stimulated with lipopolysaccharide (LPS), tumor necrosis factor alpha (TNFα), or thrombin (agents of sepsis), with/without ascorbate for 1-24 h. PAI-1 mRNA was determined by quantitative PCR. PAI-1 protein release into the culture medium was measured by ELISA. In platelets, PAI-1 release was measured after LPS, TNFα, or thrombin stimulation, with/without ascorbate. In endothelial cells, LPS and TNFα increased PAI-1 mRNA after 6-24 h, but no increase in PAI-1 release was observed; ascorbate did not affect these responses. In platelets, thrombin, but not LPS or TNFα, increased PAI-1 release; ascorbate inhibited this increase at low extracellular pH. In unstimulated endothelial cells and platelets, PAI-1 is released into the extracellular space. Thrombin increases this release from platelets; ascorbate inhibits it pH-dependently. The data suggest that ascorbate promotes fibrinolysis in the microvasculature under acidotic conditions in sepsis.